Mechanisms of propulsion in the small intestine

In sheep like in rats 2 hr after feeding and in fasting dogs, the rate of passage of digesta along the small intestine is related to the migration of the myo-electric complexes (MMCs). The modifications of this basic common pattern and that of its two consecutive irregular and regular phases were related to changes in the flow of digesta in both the proximal and distal parts of the small intestine. A high flow rate in the jejunum is associated to an increase in duration of the phases of ISA and by supernumerary MMCs at this level. Normally at the ileal level, the flow of digesta was lower than in upper parts with an increase in retention time associated both with a slow migration of the complexes and the disappearance of about one third of them after traversing 60% of the length of the small bowel. These experiments suggest that the origin, propagation and frequency of the basic MMC pattern as well as the ratio of ISA to quiescence are operative factors involved in small intestine propulsive activity. The continuous spiking activity seen immediately after feeding in rats and dogs and the autonomous pattern of activity of the ileum during prolonged fasting in sheep represent extreme changes of the basic MMC pattern.